In vertebroplasty, the surgeon seeks to treat a compression fracture of a vertebral body by injecting bone cement such as polymethylmethacrylate (PMMA) into the fracture site. In one clinical report, investigators describe mixing two PMMA precursor components (one powder and one liquid) in a dish to produce a viscous acrylic bone cement; filling 10 ml syringes with this cement, injecting it into smaller 1 ml syringes, and finally delivering the mixture into the desired area of the vertebral body through needles attached to the smaller syringes. Jensen AJNR: 18 Nov. 1997,
Kyphoplasty is a method of practicing vertebral body augmentation in which a space is created in the fractured vertebral body in order to receive a bulking agent. The creation of such a space enhances the safety of the procedure, as the cement may be injected under low pressures. The cavity also creates a region of least resistance to cement flow, thereby lowering the risk of cement extravasation. Preferably, this space-creating technology may also restore at least a portion of any lost height in the vertebral body. In one such kyphoplasty technique, U.S. Pat. No. 5,108,404 (“Scholten”) discloses inserting an inflatable device such as a balloon within a passage within the vertebral body, inflating the balloon to compact the surrounding cancellous bone and create an enlarged void in the vertebral body, and finally injecting bone cement into the void.
There is a desire to develop technologies that can create a space in a fractured vertebral body without using a balloon in order to deliver cement into the space in the vertebral body.
Expandable screws enjoy a positive clinical history and are indicated for use in spinal surgery. Expansion screws have clinical familiarity and are known in the practice of spinal medicine. Expanding pedicle screws have been used to compact trabecular bone within screw threads in an attempt to prevent screw pull-out or mechanical failure in osteoporotic patients with good results. Cook, J Spinal Disorders 13(3) 230-36, 2000. Similarly, cementation of pedicle screws in osteoporotic bone has been investigated with good results. Frankel, Neurosurgery, 61(3) 531-9, 2007.
Numerous patents and patent applications disclose the use of expandable screws for reducing fractured bones. See, for example, U.S. Pat. No. 2,381,050; U.S. Pat. No. 4,091,806; U.S. Pat. No. 4,760,843; and U.S. Pat. No. 5,209,753; U.S. Pat. No. 6,436,142; U.S. Pat. No. 5,704,936; US Patent Publication No. US2007-0233250; US Patent Publication No. US2007-0233249; and US Patent Publication No. US2009-0264941.